The continuing saga of soy

by KIM N. ARREY  November 2012

Soy foods can be an important source of plant protein that is low in calories and fat, and cholesterol-free. Some studies suggest that soy foods can play a role in preventing cancer. Other studies are finding that the type of soy product consumed and how it is cooked can also influence the risk of developing cancer.

Breast cancer

For many years, scientists have speculated on the mechanisms by which soy isoflavones act to protect against breast cancer. A study published in 2012 suggests a new mechanism whereby the soy isoflavones interrupt the methylation of DNA in BRCA1 and BRCA2 genes.1 This actually “turns on” the genes so that they protect against the development of breast cancer tumours.

Another study has suggested that soy isoflavones act differently.2 In vitro, soy isoflavones act on breast cancer stem cells and limit their growth and ability to reproduce. It also reduces their ability to clump together to form mammospheres.

Lung cancer

A recent article reviewed the epidemiologic data linking soy to the prevention of lung cancer.3 It found that the highest consumption of soy products was associated with a 23 percent decrease in the risk of developing lung cancer. This effect was greater in women, people who had never smoked and individuals of Asian ethnicity. This study also showed that soy’s protective effect was greater when non-fermented products like soy milk and tofu were consumed. On the other hand, eating fermented soy products such as miso and natto reduced the protective effect.

Gastric cancer

Another review article looked at the influence that consuming soy products had on the risk of developing gastric cancer.4 It found that in general, including soy in the diet was associated with a decreased risk of developing gastric cancer. But again, the risk varied depending on the type of soy products. The article reported that those who ate more fermented products, like miso and natto, had a 22 percent higher risk of developing gastric cancer, while people who consumed non-fermented products like tofu and soy beverage had a 36 percent lower risk.

Food prep

A study published in June 2012 suggests that the way soy foods are prepared can influence how they affect cancer cells. This study showed that in vitro, an extract of cooked soybeans had a greater apoptotic effect than that of uncooked soybeans.5 This study also showed that the amount of genistein in the soy extract was reduced after heating for 30 minutes, while the amount of the other isoflavones increased.

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